The present invention relates to a bicycle speed control, and more particularly to improvements in a multi-step type of speed change lever which cooperates with a rear derailleur and a multi-speed free wheel assembly having a plurality of sprocket wheels of different diameter mounted on a rear axle of a bicycle, in order to switch over the running drive chain from one sprocket wheel to another for effecting the desired speed change.
It is well known to those skilled in the art that, in the speed change operation of a bicycle, it is desirable to make the drive chain intentionally over-shifted to such a position slightly beyond the position just under a sprocket wheel onto which the chain is to be switched over. By over-shifting the chain in this way, the chain is permitted to smoothly and quickly switched over onto a desired sprocket wheel without disengagement from the free wheel assembly.
Further, in case the drive chain is switched over from a smaller sprocket wheel onto a larger one, it is desirable to return the chain slightly back from the initial over-shifted position immediately, because the chain is likely to undersirably come into contact with a side wall of an adjacent larger sprocket wheel unless the chain is returned back immediately from the initial over-shifted position.
In the operation of a stepless type of bicycle speed change lever the above-discussed over-shifting and returning of the drive chain can be easily attained, although it is difficult to shift the chain quite accurately. On the other hand, the multi-step type of bicycle speed change lever is advantageous in accurate positioning of the drive chain, but it is very difficult to perform the above-discussed over-shifting and returning of the chain because of its particular construction in which the lever positions are fixed stepwise. Description on this point will now be made more in detail with reference to FIG. 9 of the accompanying drawings which diagrammatically illustrates the conventional chain shifting manners, in which reference numerals I, II, III, IV, V respectively designate positions just under each of the sprocket wheels of the five-speed free wheel assembly, and reference characters P.sub.a, P.sub.b, P.sub.c, P.sub.d, P.sub.e, respectively designate predetermined chain stop positions over-shifted by a distance o. In case the lever is operated to shift the chain from a smaller sprocket wheel to a larger one, that is, in the direction of an arrow L in FIG. 9, the chain is desirably over-shifted by the distance o. However, in case the lever is operated in the reverse direction to shift the chain in the direction of an arrow S, the smooth and quick switching of the chain cannot be achieved, because the chain shift is naturally insufficient by the distance o. In othe words, the chain in this case is arranged to stop at one of the predetermined stop positions P.sub.a, P.sub.b, P.sub.c, P.sub.d, P.sub.e which lie short by the distance o of the positions I, II, III, IV, V, respectively, which are just under the sprocket wheels.
Further, even in case the lever is operated to shift the chain in the direction of the arrow L, the conventional bicycle speed change lever is not so designed as to permit a slight returning of the over-shifted chain toward the positions I, II, III, IV, or V, and , therefore, the over-shifted chain is inclined to undesirably come into contact with a side wall of a next larger sprocket wheel to the sprocket wheel onto which the chain is to be engaged, causing unpleasant noise and damage by abrasion with the chain and sprocket wheels.
Accordingly it is an object of the present invention to eliminate the above-discussed deficiencies in the conventional multi-step type bicycle speed change lever.
Another object of the invention is to provide an improved multi-step type bicycle speed change lever which permits a suitable distance of over-shifting of the bicycle drive chain not only in the case where the chain is switched over from a smaller sprocket wheel to a larger one but also in the reverse case, so that the bicycle speed change performance can be always carried out quickly and smoothly.
Other objects, features and advantages of the present invention will become apparent from the detailed description given hereinafter; it should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.